def setup():
    size(600, 600)
    rectMode(CENTER)
    colorMode(HSB)

def draw():
    background(0)
    translate(20, 20)
    for x in range(30):
        for y in range(30):
            d = dist(30 * x, 30 * y, mouseX, mouseY)
            fill(0.5 * d, 255, 255)
            rect(30 * x, 30 * y, 25, 25)
